Apparatus for chlorination reactions



Dec. 16, 1952 1.. A. MILLER ETAL 2,622,205

APPARATUS FOR CHLORINATION REACTIONS Original Filed May 10, 1949 3Sheets-Sheet l FIGURE 2 II IO FIGURE INVENTORS JAMES H. DUNN LEO A.MILLER CLARENCE M. NEHER Dec. 16, 1952 A. MILLER ETAL APPARATUS FORCHLORINATION REACTIONS Original Filed May 10, 1949 3 Sheets-Sheet 2 J a34; g d i 1 .2? H1 4 (J x'l m 0 r--- I,

Q I LL r 1- w \J V a INVENTORS JAMES H. DUNN LEO A. MILLER Dec. 16, 1952L. A. MILLER EIAL 2,622,205

APPARATUS FOR CHLORINATION REACTIONS Original Filed May 10, 1949 3Sheets-Sheet 3 FIGURE 4 AVERAGE DENSITY CORRECTION-REFERRED T0 DEGREES CGRAMS PER CUBIC CENTIMETER PER DEGREE C TEMPERATURE, DEGREES 0 FIGURE 5INVENTORS JAMES H. DUNN LEO A. MILLER BY CLARENCE M. NEHER Patented Dec.16, 1952 APPARATUS FOR CHLORINATION REACTIONS Leo A. Miller, James H.Dunn, and Clarence M. Neher, Baton Rouge, La., assignors to EthylCorporation, New York, N. Y., a corporation of Delaware Originalapplication May 10, 1949, Serial No. 92,266. Divided and thisapplication December 9, 1950, Serial No. 200,002

2 Claims.

This application is a division of our copending application Serial No.92,266 filed May 10, 1949.

This invention relates to the manufacture of chlorinated hydrocarbonsand apparatus for the manufacture thereof. In particular, the inventionis concerned with the manufacture of henzene hexachloride and a new andimproved method of carrying out the formation reaction.

Benzene hexachloride, CcHsCle, also called hexachlorocyclohexane orGammexane, is an important industrial chemical. Its insecticidalpotency, particularly of the gamma isomer, is well known. It has beenknown for a long period that benzene hexachloride could be produced bythe complete addition chlorination of benzene. However, no fullysatisfactory method has as yet been disclosed for this reaction.

An object of the present invention is to provide a new and improvedreaction technique. An additional object is to overcome some of thespecifie deficiencies of the prior art. A further object is to providean efficient continuous process and apparatus for carrying out theprocess. A still further object is to provide a higher degree ofconversion of benzene to benzene hexachloride.

The principal reaction method of the prior art involves the batchwisephotochemical chlorination of benzene in a reaction pot or vessel. Thechlorination is continued until the quantity of benzene hexachlorideproduced is sufficient to exceed the solubility in benzene, and a largeproportion of benzene hexachloride formed is present in the solid phase.Chlorination is then stopped and the mixture of unreacted benzenedissolved and solid benzene hexachloride removed from the reactor. Thesolids are separated by filtration, the liquid or filtrate being thencombined with fresh benzene and returned to the chlorination step.

The above reaction method, although it has been commercially used, isfar from being entirely satisfactory. A particular disadvantage of themethod is the physical condition of product mixture resulting. A mixtureof solids and liquids is of course more difiicult to handle than aliquid system. In the manufacture of benzene hexachloride thedisadvantage of a mixture of solids and liquids is even more pronounced.The crystals of benzene hexachloride tend to deposit in the equipmentand to cause plugging of pumps, valves and lines. Thus, the reactedmixture is quite unsuitable for product separation and recovery. Afurther disadvantage of the prior art method is the frequent necessityof discarding large amounts of the reactor solution. This wastefuloperation is necessitated because the recovery method is predicated uponthe formation of a separate solid product in the reactor proper. Theeffect of this technique is to cause a build up in concentration of anyimpurities in the reactor solution. These impurities may be normallyliquid or normally solid materials resulting from the chlorination ofimpurities in the feed benzene. As the reaction technique contemplates abenzene hexachloride recovery operation such as filtration or the like,these impurities are ordinarily removed from the system by the obviouslywasteful procedure of discarding the solution at periodic intervals.Alternatively, the benzene may be distilled off and the impuritiesseparated. This has the disadvantage of introducing another step in theoverall process.

An additional fault of the batchwise chlorination method described isthe irregular concentration of the various isomers of the product. Thisis caused by the fact that the different isomers of benzene hexachloridehave varying solubilities in benzene. Hence, in chlorinating untilsolids are formed, those first precipitated in the reactor do notcorrespond in proportions to the overall analysis of the benzenehexachloride actually formed by the reaction. This requires carefulreblending of the products in order to offer a material of uniformcomposition.

Inbrief, the prior method of making benzene hexachloride suffers thedisadvantages of producing a reaction mixture which is diflicult tohandle and process further. In addition, the technique employed requiresfrequent discard of valuable materials, or else a separate recoveryoperation to isolate unreacted benzene after interruption of thereaction. The batchwise chlorination also necessitates reblending of thefinal solid produced to obtain a uniform product.

It is an object of our invention to avoid serious difficulties of theprior art. In addition, our reaction fully meets the other objective ofproviding a continuous and highly efficient method giving a high yieldof benzene hexachloride.

These objectives are attained by controlling the proportions of chlorineand benzene present so that the existence or formation of benzenehexachloride in the solid phase is avoided. In addition, we irradiatethe reaction mixture for a relatively extended period while confiningthe mixture as a stream of limited cross sectional area. Theseconcurrent requirements are essential to the accomplishment of theobjectives of our reaction method.

In order to avoid the formation of a solid phase in the reactor, theproportion of chlorine relative to benzene is restricted. We limit theproportion of chlorine fed so that, upon complete conversion to benzenehexachloride, the solubility thereof in benzene is not exceeded at anypoint in the apparatus. Thus, the conditions are maintained so thatcrystals are not precipitated at valves. constrictions, or other pointsin the reactor.

We have found several methods of determining the specific allowable flowrate-s or ratios of chlorine and benzene in our process. Although eachof the procedures provide the same result, they differ in applicabilityand feasibility of use. Broadly speaking, the most direct methodconsists in determining the chlorinezbenzene ratio at which solidbenzene-hexachloride is first formed, and then reducing the chlorinerate a slight quantity below that value. In practice, this can be doneby operating at a specific chlorinezbenzene ratio until a steady stateis reached, then raising the chlorine flow slightly. The reactionmixture is observed closely and the cycle is repeated until solids areformed. The chlorinezbenzene ratio is then immediately reduced toprevent further formation of solid benzene hexachloride.

A preferred method of controlling the reaction employs density of thereaction solution as a control variable. It has been found that thedensity of the solution at the limiting condition, when corrected to 20C. bears a linear relationship to the solution temperature. Thislimiting relationship is expressed as d=0.8922-i0.00237 T whered=density at 20 C. in grams per cubic centimeter and T=the solutiontemperature, C.

The density, d, the control variable, is determined conveniently bymeasurement of the actual solution density with a hydrometer at anyconvenient temperature. This observed density is then corrected to thedensity at 20 C. An integrated average density correction factor isshown by Figure 5. The actual density, for our preferred conditions, isfrom 0.85 to 1.03 grams per cubic centimeter.

It has been found that the limiting density, as expressed by theequation given above, does not correspond to the density of a saturatedsolution of benzene hexachloride. Rather, this limiting density is afinite amount below that corresponding to saturation. The reason forthis difierence is not fully understood, as it might be expected that itwould be possible to chlorinate up to the saturation limit for thesolution. One possible explanation might be the existence of a slowmoving film of solution at the cooled walls of a reactor. Precipitationof benzene hexachloride crystals would probably occur because of thelower temperature at that point. By maintaining the solution density asspecified above, such difficulty is avoided.

In order to operate below the defined density limitation, We employ arelatively low chlorine to benzene feed. ratio. The density iscontrolled by varying this ratio. This is in contrast to prior methods,which taught that chlorination should be carried to as great an extentas possible. In actual operation, the determination of the density ofthe reaction mixture at only one point is usually adequate. Preferably,we measure the density of the reacted mixture leaving the reactor.

The entire reacting mixture is exposed to actinic light for an extendedperiod. A reaction period of five minutes or more is ordinarily requiredin our operation, a preferred reaction period being about 15 minutes. Inalmost every case, a reaction period of 20 minutes is adequate forrelatively complete conversion of chlorine to benzene hexachloride.

It will be noted that our method insures that every portion of thereacting mixture is irradiated for the full extended period describedabove. This assures uniform conversion of the chlorine in its passagethrough the reactor. In prior methods, stratification of the reactionmixture permits discharge of unreacted chlorine. Our method avoids thisdifficulty and assures that the chlorine is retained in the radiationzone for the full period required.

Additional requirements of our reaction method are the steps ofmaintaining the reaction mixture as a stream of limited cross sectionalarea and completely irradiating this stream with actinic light. Bycompletely irradiating we refer to transmission of actinic light throughthe entire cross section of the stream. The use of a stream ofrelatively limited cross sectional area makes possible this completeirradiation. A further advantage of a limited cross sectional area isthe avoidance of stratification, so that the reaction mixture is uniformat any given cross section. Our reaction stream may be maintained inrectangular, circular, square, or annular cross section. Other irregularcross sections are quite suitable. We have found that, with thepreferred light sources, the cross section should ordinarily have ahydraulic radius not in excess of 1.5 inches. This figure is not,however, an absolute limitation, as even larger streams can be utilizedwhen an especially intense actinic light source is available. Apreferred size of reaction stream, particularly suited for use withcurrently available actinic light sources, is a stream with a hydraulicradius of 0.75 inch. Smaller streams are satisfactory, but as apractical matter, we have found it preferable not to go below a streamwith a hydraulic radius of 0.5 inch.

A variety of embodiments of our invention is possible, providing thatthe limitations heretofore stated are adhered to. The accompanyingfigures illustrate several embodiments and means of carrying out theinvention. Figure 1 is an elevation View of a preferred embodimentutilizing a reactor conduit of high capacity. Figure 2 shows atransverse section of a reactor conduit along line 2-2 of Figure 1 aswell as means of supplying actinic light to the reaction mixture. Figure3 illustrates an embodiment carried out in a more economicallyconstructed reactor. Figure 4 shows a transverse section of the reactorof Figure 3 along lines a. In Figure 5, a density correction factor isgraphically shown.

Referring to Figure 1, this embodiment employs a reactor comprising anextended cylindrical conduit transmissive of actinic light. Chlorine gasis fed to the unit through line If). the flow being controlled by valveH. A liquid stream predominating in benzene is fed through line I2, therate of fiow being controlled by valve 13. The chlorine and benzenecontaining stream mix in line [4, the chlorine dissolving in thebenzene. The mixture then immediately flows to the reactor. The reactoris composed of a lar fluorescent lights series of light transmissivetubes I5 connected by return bends [6.

The reaction mixture is subjected to the action of actinic lightradiated by fluorescent lights II. In passing through the conduit, thechlorine is completely converted to benzene hexachloride by reactionwith the benzene.

The reacted mixture, comprising benzene and benzene hexachloride isdischarged from the reactor through line l3 and fiows to suitablerecovery operations. The temperature of the reaction mixtures can bemeasured by several temperature indicators [9. Samples are withdrawn formeasurement of density through sample connections 20. Density of thesolution in quite simply adjusted by increasing or decreasing thechlorine feed rate while keeping the benzene rate constant.

The reaction of benzene and chlorine liberates appreciable quantities ofheat which must be dissipated in part from the liquid phase. Coolingwater is fed to the unit through line 28 and valve 2 I, to adistributing trough 22. Trough 22 is merely a V trough in which Waterflows over the edges 23 and drips from a notched distributor plate 24which is aligned above the reaction tube [5.

Figure 2 is a transverse sectional view 2-2 of the reaction conduit ofFigure 1. In this embodiment the preferred light sources are tubullemitting white light varying from 4000 to 7000 angstrom units. Thepreferred disposition of the lights is such that the cooling water 21forms a' continuous peripheral steam around the reaction conduit l5. Theconduit I5 is filled or substantially filled with the reacting mixturein liquid phase 25 as indicated. A small amount of vapor 26 is formed,the quantity dependent on the temperature and possible substitutionchlorination of impurities in the benzene, resulting in hydrogenchloride formation.

A second embodiment of our invention is shown by Figures 3 and 4. Figure3 is a plan view of the reactor. The reactor of the present embodimentdiffers from the reactor of Figure 1 in that it is of unitaryconstruction. The reactor is essentially a cast concrete slab 50 with areaction channel 52 cast therein. Referring to Figure 4, a transversesection 4-4 of the reactor, the reaction conduit 52 is completed by acover 5| of glass or other material transmissive of actinic light. Thechannels 52 in the concrete are preferably sealed with an imperviouscoating of carbon-phenolic resin cement or other impermeable material.The light transmissive cover 5| is preferably secured in place with alayer of impervious cement 54. The conduits 52 are preferably coatedwith a lining of impervious cement 53. Light sources are not shown byFigures 3 and 4. In this embodiment they are suspended above the lighttransmissive cover 5| by any convenient means.

The reaction in the present apparatus is carried out in much the samemanner as in the reactor of Figure 1. Chlorine gas is fed through line'55 and valve 56 and admixed with a predominantly benzene solution fedthrough line 51 and valve 58. The mixture is fed to conduit 52 throughline 59.

The reaction occurs as in the reactor of Figure 1, a certain amount ofvaporization occurring. The present reactor is not as efficiently cooledas a react-or cooled around its entire periphery. However, as explainedhereafter, temperature is not a critical factor in the reaction. Heatr-' moval is accomplished by flow of cooling water 60 across the glasscover 5|, the water being supplied by pipe 65. For operation at highcapacity, a cooling tube 64 can be built into the conduit 52. Thereacted mixture is discharged from the conduit 52 through line 6|,temperature being observed by indicator 62. Samples are removed bysample connection 63, for measurement of the density for controlpurposes.

The temperature at which we carry out the reaction is not criticalalthough it is important. We have found that temperature has very littleeffect on reaction rate, which is contrary to published information(Slator, Journal of the Chemical Society 83, p. 729 et seq.). However,we have found that it is ordinarily preferable to maintain the solutiontemperature at not over C. Operating at a temperature above 80 C.necessitates pressure operation to maintain the reacting mixturesubstantially in the liquid phase. With respect to low temperatures, weare able to operate successfully at temperatures approaching thefreezing point of benzene. However, for practical operation, it ispreferred to operate above 20 C., because of the much greater tendencyto form solids at temperatures below 20 C.

It will be noted that the use of a reaction stream of restricted crosssection, as utilized in our method, possesses the additional advantagethat temperature is easily controlled.

The pressure of operation is not a limiting factor as the desiredreaction occurs in the liquid phase. For practical convenience, we havefound that an operating pressure slightly above atmospheric ispreferred. Operating pressures which are much higher than 15 pounds persquare inch should not ordinarily be used, as they introduce numerouspractical engineering problems. The preferred range is 5 to 15 poundsper square inch, dependent on the pressure drop at the operating rate.

The benzene feed stream may be pure benzene or may contain appreciableamounts of dissolved benzene hexachloride. The permissible use of arecycled dilute solution of benzene hexachloride is especially useful incontinuous operations. A basic requirement of our reaction method isthat a relatively large proportion of benzene is fed. Hence, substantialamounts of benzene are recycled after removal of all or a part of thebenzene hexachloride content of the outlet stream. The preferredcomposition of the benzene feed stream is less than 15 per cent benzenehexachloride. It is ordinarily uneconomical and unnecessary for thebenzene hexachloride content to be less than 2 per cent benzenehexachloride.

The benzene hexachloride in the product solution from our reaction canbe recovered in several ways known to the art. For example, steamdistillation is a suitable method of separation. An especiallyadvantageous method comprises vaporizing the benzene at relatively lowtemperature, and using the benzene hexachloride at a temperature of overC.

The reaction can be maintained by various types of actinic light.Sunlight, ultraviolet light, or the irradiation from a carbon are aresuitable. The effectiveness of different types of light is attributed tothe wide spread of spectral absorption by chlorine. Although variousforms of actinic light thus can be used, we have found that a preferredlight source is fluorescent tubular lights emitting white light. Theselight sources give forth light ranging between 4000 and 7000 angstromuni-ts. The preferredin-tensity of such light is that produced byWattage of from to per lineal foot of reaction conduit.

The following is a full scale operation of our reaction method. Thereactor used in thi example corresponds in general design to the'desig-nillustrated by Figure l and Figure 2, heretofore described. The reactorisfabricated of hero-silicate heat resistant glass and was uniformly 3inches in inside diameter. The irradiated reaction section was 120 feetlong.

The benzene feed, consisting of 12 pounds per hour of nitration gradebenzene is mixed with 1165 "pounds of a recycle benzene streamcontaining 6.5 per cent benzene hexachloride. Chlorine is mixed withthis stream at the rate "of 32 pounds per hour. The total feed to thereactor is then 1209 pounds per hour, containin 91 per cent benzene, 6.3per cent benzene hexachloride and 2.7 per cent chlorine. The residencetime in the reactor is approximately 19 rninutes. The reaction isinitiated and maintained by light predominantly in the 4000 to 7000angstrom unit range. The chlorine feed is approximately 97 per centconverted to benzene hexachloride, giving a reactor product mixturecontaining 9.8 per cent benzene hexachloride.

The reaction temperature is 57 C. in the first section of the reactorand the discharge temperature is 40 C. At this discharge temperature,the limiting operating density, corrected to 20 C. is 0.987 gram percubic centimeter. The actual density of the outlet stream, at 40 C., is0.961 gram per cubic centimeter. The average density correction factor,from Figure 5, is 0.00107 gram per cubic centimeter per C., giving atotal correction of 0.021. The density of the reactor product mixture,corrected to 20 C., is thus 0.94, which is well below the limitingdensity of 0.987. No solids were formed at any point in the reactor andthe reactor product was a solid-free, clear solution.

The foregoing is an example of operation at a very low rate. Much higherproduction rates can be attained in the same apparatus. For example, '73pounds per hour of fresh benzeneand 193 pounds of chlorine are mixedwith 2000 pounds of a recycle benzene stream containing 13 per centbenzene hexachloride. This mixture is fed to the same reactor as used'inthe foregoing example. At the present high feed rate, the reactiontemperatures are substantially higher; varying from t'o 50 C. Theconversion of chlorine to benzenehexaohloride is overper cent as in thepreceding example.

Having fully described our invention and the manner of operation, itwill be apparent to one skilled in the art that numerous embodiments canbe utilized in addition to those illustrated herein.

We claim:

1. Photochemical halogenating apparatus comprising'a molded slab ofplastic material having an exposed surface, a channel molded into saidslab surface for providing an exposed conduit in which photochemicalhalogenation can take place, a transparent cover sealed to said surfaceand enclosing the channel for confining the halogenation materials inthe channel and simultaneously exposin them for actinic illumination;and cooling structure including fluid-discharge elements connected fordischarging and flooding over said cover a quantity of coolant fluid.

2. The combination as defined by claim 1 in which-the plastic materialis concrete and the conduit is of a sinuous shape.

LEO A. MILLER. JAMES H. DUNN. CLARENCE M. NEHER.

REFERENCES CIT-ED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,456,366 Sconce et al Feb. 17,1948 2,528,320 Roberts et al Oct, 31, 1950

1. PHOTOCHEMICAL HALOGENATING APPARATUS COMPRISING A MOLDED SLAB OFPLASTIC MATERIAL HAVING AN EXPOSED SURFACE, A CHANNEL MOLDED INTO SAIDSLAB SURFACE FOR PROVIDING AN EXPOSED CONDUIT IN WHICH PHOTOCHEMICALHALOGENATION CAN TAKE PLACE, A TRANSPARENT COVER SEALED TO SAID SURFACEAND ENCLOSING THE CHANNEL FOR CONFINING THE HALOGENATION MATERIALS INTHE CHANNEL AND SIMULTANEOUSLY EXPOSING THEM FOR ACTINIC ILLUMINATION;AND COOLING STRUCTURE INCLUDING FLUID DISCHARGE ELEMENTS CONNECTED FORDISCHARGING AND FLOODING OVER SAID COVER A QUANTITY OF COOLANT FLUID.